Frequent Regular Expressions

Here are some frequently used regular expressions.

IP Address:
^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$

Social Security Number:
^\d{3}-?\d{2}-?\d{4}$

Credit Card: [Visa, MC, AmEx, and Discover]
^(?:4[0-9]{12}(?:[0-9]{3})?|5[1-5][0-9]{14}|6(?:011|5[0-9][0-9])[0-9]{12}|3[47][0-9]{13}|3(?:0[0-5]|[68][0-9])[0-9]{11}|(?:2131|1800|35\d{3})\d{11})$

Use Luhn algorithm to check if a credit card number is a valid number. Of course, the algorithm doesn't obviously check if the card is actually any good. Such must be checked with the card issuer.